Decomposing system for polyisocyanate residues, and start-up method for the same

ABSTRACT

An object of the invention is to provide a decomposing system for polyisocyanate residues that is capable of suppressing reaction of polyisocyanate residues with high temperature and high pressure water to allow smooth start-up of the operation, and a start-up method for the decomposing system for the polyisocyanate residues. The decomposing system is used for hydrolyzing the polyisocyanate residues to polyamine using high temperature and high pressure water, comprising a hydrolyzer, a water feed pipe connected to the hydrolyzer, a residual feed pipe connected to the water feed pipe, a solvent feed line for filling an organic solvent in a solvent filling portion of the residual feed pipe, and a solvent draining line. Upon start-up of the operation, the organic solvent is previously filled in the solvent filling portion via the solvent feed line and the solvent draining line, first, and then, the high temperature and high pressure water is fed from the water feed pipe to the hydrolyzer. Then, the organic solvent is fed from the residual feed pipe to the water feed pipe, first, and then, the polyisocyanate residues are fed thereto.

The present invention is a Divisional Application of U.S. applicationSer. No. 11/988,678, filed Jan. 11, 2008, which is the National Stage ofInternational Application No. PCT/JP2006/314214, filed Jul. 12, 2006,and claims foreign priority to Japanese Application No. 2005-203222,filed Jul. 12, 2005, the entire contents of each of which areincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a decomposing system for decomposingpolyisocyanate residues to polyamine using high temperature and highpressure water, and a start-up method for the same.

BACKGROUND ART

Polyisocyanate, used as a raw material of polyurethane, is industriallyproduced, for example, by allowing polyamine to react with carbonylchloride, for isocyanate reaction.

In this producing plant of polyisocyanate, after completion of theisocyanate reaction, high-molecular-weight polyisocyanate, which is abyproduct produced during the production, is separated from the crudepolyisocyanate obtained.

In recent years, it has been proposed that the residues secondarilyproduced are continuously fed to a reactor vessel in its liquid state,while also high temperature and high pressure water is continuously fedto the reactor vessel, with temperature of the reactor vessel controlledto 190-300° C., whereby the residues are decomposed to polyamine so thatthe polyamine obtained can be reused (cf. Patent Document 1 cited below,for example).

[Patent Document 1] Japanese Unexamined Patent Publication No.10-279539.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, in the method described by Patent Document 1 cited above, thehigh temperature and high pressure water is continuously fed to thereactor vessel through another line separate from a residual feed line,so that the residues and the high temperature and high pressure waterare first brought into contact with and mixed with each other in thereactor vessel.

However, this conventional method has the disadvantage that when gettingcontact with each other in the reactor vessel, the residues and the hightemperature and high pressure water cannot be mixed with each otherpromptly and thoroughly, due to their substantial differences in theirown nature.

Patent Document 1 cited above also describes that the high temperatureand high pressure water may be made to flow into the residual feed linebefore the residues are introduced in the reactor vessel.

However, in the case that the high temperature and high pressure wateris made to flow into the residual feed line, neither a linear velocityof the feed line nor a temperature rise of the residues is sufficient ata confluence portion upon start-up of an operation, due to which theresidues and the high temperature and high pressure water are put inprolonged contact with each other before introduced in the reactorvessel. As a result, many intermediate products, including an ureacompound and so on, are produced by the reaction of the residues and thehigh temperature and high pressure water and solid materials growing outof an urea compound and so on are produced, causing a possible blockageof the feed line.

It is an object of the present invention to provide a decomposing systemfor polyisocyanate residues that is capable of suppressing reaction ofpolyisocyanate residues with high temperature and high pressure water toallow smooth start up of decomposition of the polyisocyanate residues.It is another object of the present invention to provide a start upmethod for the decomposing system for the polyisocyanate residues.

Means for Solving the Problem

The present invention provides a start-up method for a decomposingsystem for decomposing polyisocyanate residues to polyamine using hightemperature and high pressure water, the decomposing system comprising adecomposing tank for allowing polyisocyanate residues and hightemperature and high pressure water to contact with each other, a waterfeed pipe, connected to the decomposing tank, for feeding the hightemperature and high pressure water to the decomposing tank, and aresidual feed pipe, connected to the water feed pipe, for feeding thepolyisocyanate residues to the decomposing tank together with the hightemperature and high pressure water, wherein a solvent is previouslyfilled in a connecting portion of the residual feed pipe with the waterfeed pipe, first, and then, the high temperature and high pressure wateris fed from the water feed pipe to the decomposing tank, then, thesolvent being fed from the residual feed pipe to the water feed pipe,first, and then, the polyisocyanate residues being fed thereto.

According to the start-up method for the decomposing system for thepolyisocyanate residues of the present invention, upon the start-up ofthe operation, the solvent is first fed from the residual feed pipe tothe water feed pipe via which the high temperature and high pressurewater is fed to the decomposing tank. Then, a supply flow from theresidual feed pipe to the water feed pipe is formed. Due to this, whenthe polyisocyanate residues are subsequently fed from the residual feedpipe, the polyisocyanate residues are smoothly fed to the water feedpipe at a sufficient linear velocity, going along the supply flowthereof. Thus, the polyisocyanate residues are fully mixed with the hightemperature and high pressure water at the confluence portion and thenfed to the decomposing tank, without stay at the confluence portion.This can prevent a blockage caused by the production of solid materialsgrowing out of an intermediate product produced by the reaction of thepolyisocyanate residues and the high temperature and high pressurewater, and can allow smooth start-up of the operation.

Further, in this method, it is preferable that the decomposing systemcomprises opening and closing unit (preferably flash opening and closingunit) interposed in the residual feed pipe at an end thereof connectingwith the water feed pipe, and residual transporting unit interposed inthe residual feed pipe at a location thereof on the upstream side of theopening and closing unit, that part of the residual feed pipe extendingat least between the opening and closing unit and the residualtransporting unit serves as the connecting portion in which the solventis filled, that the connecting portion is increased in its innerpressure by transporting the solvent or the polyisocyanate residues tothe connecting portion by the residual transporting unit in the state ofthe opening and closing unit being closed, and that the high temperatureand high pressure water is fed from the water feed pipe to thedecomposing tank, and after a decomposing temperature and a decomposingpressure of the decomposing tank reach a predetermined decomposingtemperature and a predetermined decomposing pressure, the opening andclosing unit is opened to feed the solvent from the residual feed pipeto a confluence portion thereof with the water feed pipe, first, andthen, the polyisocyanate residues are fed thereto.

By feeding the polyisocyanate residues in this manner, a blockage causedby the production of solid materials growing out of an intermediateproduct produced by the reaction of the polyisocyanate residues and thehigh temperature and high pressure water can be prevented moreeffectively, thus allowing smooth start-up of the operation.

The present invention provides a decomposing system for polyisocyanateresidues comprising a decomposing tank for allowing polyisocyanateresidues and high temperature and high pressure water to contact witheach other, a water feed pipe, connected to the decomposing tank, forfeeding the high temperature and high pressure water to the decomposingtank, a residual feed pipe, connected to the water feed pipe, forfeeding the polyisocyanate residues to the decomposing tank togetherwith the high temperature and high pressure water, and solvent fillingunit, interposed in the residual feed pipe at a portion thereofconnecting with the water feed pipe, for filling the solvent in it.

According to the decomposing system for the polyisocyanate residues ofthe present invention, upon the start-up of the operation, the solventis previously filled in the connecting portion of the residual feed pipewith the water feed pipe by the solvent filling unit. Then, the hightemperature and high pressure water is fed from the water feed pipe tothe decomposing tank. Thereafter, the solvent is fed from the residualfeed pipe to the water feed pipe, first, and then, the polyisocyanateresidues are fed thereto. This means that upon start-up of theoperation, the solvent is fed from the residual feed pipe to the waterfeed pipe via which the high temperature and high pressure water is fedto the decomposing tank. Then, a supply flow from the residual feed pipeto the water feed pipe is formed. Due to this, when the polyisocyanateresidues are subsequently fed from the residual feed pipe, thepolyisocyanate residues are smoothly fed to the water feed pipe at asufficient linear velocity, going along the supply flow thereof. Thus,the polyisocyanate residues are fully mixed with the high temperatureand high pressure water at the confluence portion and then fed to thedecomposing tank, without stay at the confluence portion. This canprevent a blockage caused by the production of solid materials growingout of an intermediate product produced by the reaction of thepolyisocyanate residues and the high temperature and high pressurewater, and can allow smooth start-up of the operation.

It is preferable that this system further comprises opening and closingunit (preferably flash opening and closing unit), interposed in theresidual feed pipe at an end thereof connecting with the water feedpipe, and residual transporting unit provided in the residual feed pipeat a location thereof on the upstream side of the opening and closingunit, and that part of the residual feed pipe extending at least betweenthe opening and closing unit and the residual transporting unit servesas the above-mentioned connecting portion in which the solvent isfilled.

It is preferable that the solvent is filled in the part between theresidual transporting unit and the opening and closing unit, for afurther stable start-up of the operation.

According to this system, the solvent or the polyisocyanate residues aretransported by the residual transporting unit in the state of theopening and closing unit being closed, whereby the inner pressure of theconnecting portion is increased. The high temperature and high pressurewater is fed from the water feed pipe to the decomposing tank, and aftera decomposing temperature and a decomposing pressure of the decomposingtank reach a predetermined decomposing temperature and a predetermineddecomposing pressure, the opening and closing unit is opened to feed thesolvent from the residual feed pipe to a confluence portion thereof withthe water feed pipe, first, and then, the polyisocyanate residues arefed thereto. This can further effectively prevent a blockage caused bythe production of solid materials growing out of an intermediate productproduced by the reaction of the polyisocyanate residues and the hightemperature and high pressure water, and can allow smooth start-up ofthe operation.

Effect of the Invention

When a start-up method for a decomposing system for polyisocyanateresidues of the present invention is adopted in the decomposing systemfor polyisocyanate residues of the present invention, a blockage causedby production of solid materials growing out of an intermediate productproduced by reaction of the polyisocyanate residues and high temperatureand high pressure water can be prevented to allow smooth start-up of theoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing an embodiment of adecomposing system for polyisocyanate residues of the present invention.

EXPLANATION OF LETTERS OR NUMERALS

-   1: Decomposing system-   2: Hydrolyzer-   3: Water feed pipe-   4: Residual feed pipe-   5 a: Solvent feed line-   5 b: Solvent drain line-   6: Solvent filling portion-   10: Residual pressure-feed pump-   12: Flash opening and closing valve

EMBODIMENT OF THE INVENTION

FIG. 1 is a schematic block diagram showing an embodiment of adecomposing system for polyisocyanate residues of the present invention.

In FIG. 1, a decomposing system 1 is equipped in the producing plant forpolyisocyanate, for the purpose of decomposing polyisocyanate residues(distillation residues) to polyamine using high temperature and highpressure water, in the subsequent process of a producing process ofproducing polyisocyanate and a refining process of extractingpolyisocyanate from the crude polyisocyanate (unrefined polyisocyanate)produced in the producing process by distillation operation and the liketo separate polyisocyanate from residues (hereinafter referred to aspolyisocyanate residues). The decomposing system 1 includes a hydrolyzer2 served as a decomposing tank, a water feed pipe 3 connected to thehydrolyzer 2, a residual feed pipe 4 connected to the water feed pipe 3,a solvent feed line 5 a serving as solvent filling unit for fillingorganic solvent in a solvent filling portion 6 mentioned later, and asolvent drain line 5 b.

The hydrolyzer 2 is a reactor for polyisocyanate residues to behydrolyzed to polyamine by contact of the polyisocyanate residues withhigh temperature and high pressure water. It comprises a heat-resistantand pressure-resistant vessel whose temperature and pressure can becontrolled.

The water feed pipe 3 is a water feed line for feeding high temperatureand high pressure water to the hydrolyzer 2. It comprises aheat-resistant and pressure-resistant pipe whose downstream end isconnected to the hydrolyzer 2 and whose upstream end is connected to awater feed line for feeding water (recovered process water orion-exchange water) not shown.

A water pressure-feed pump 7 for pressure-transporting the hightemperature and high pressure water toward the hydrolyzer 2 isinterposed in the water feed pipe 3. A water heater 8 is interposed inthe water feed pipe 3 at a location on the downstream side of the waterpressure-feed pump 7.

The residual feed pipe 4 is a residual feed line for feeding thepolyisocyanate residues to the hydrolyzer 2 together with the hightemperature and high pressure water. It comprises a heat-resistant andpressure-resistant pipe whose downstream end is connected to the waterfeed pipe 3 at a location on the downstream side of the water heater 8and whose upstream end is connected to a residual polyisocyanate drum 9.

The polyisocyanate residues separated in the refining process from thecrude polyisocyanate which includes high-molecular-weight polyisocyanateproduced in the polyisocyanate producing process is temporality held inthe residual polyisocyanate drum 9.

The polyisocyanate residues, which are content of tar containingprimarily high-molecular-weight polyisocyanates produced secondarily inthe production process, include dimer, trimer, multimeric-polyisocyanateand so on which comprises carbodiimide, uretodion, isocyanurate anduretoneimine.

Polyisocyanates that depend on polyisocyanate produced by a producingplant include, for example, polymethylenepolyphenylene polyisocyanate(MDI), tolylene diisocyanate (TDI), xylylenedi isocyanate (XDI),tetramethylxylylene diisocyanate (TMXDI), bis(isocyanatomethyl)norbornane (NBDI), 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate (IPDI), 4,4′-methylenebis(cyclohexylisocyanate) (H₁₂MDI),bis(isocyanatomethyl) cyclohexane (H₆XDI), and hexamethylenediisocyanate (HDI).

In order to secure fluidity of the polyisocyanate residues, thepolyisocyanate residues can be previously adjusted in viscosity byallowing a part of polyisocyanate to coexist with it or by using anorganic solvent (e.g. monochlorobenzene and dichlorobenzene) used as areaction solvent in the production process of polyisocyanate.

A residual pressure-feed pump 10, serving as residual transporting unitfor pressure-transporting the polyisocyanate residues toward the waterfeed pipe 3, is interposed in the residual feed pipe 4. For example, amultistage diaphragm pump is used as the residual pressure-feed pump 10.A residual heater 11 is interposed in the residual feed pump 4 at alocation on the downstream of the residual pressure-feed pump 10.

Also, a flash opening and closing valve 12, serving as opening andclosing unit (flash opening and closing unit), is interposed in theresidual feed pipe 4 at a location thereof on the downstream side of theresidual pressure-feed pump 10 and at an end thereof to connect with thewater feed pipe 3.

The solvent feed line 5 a and the solvent drain line 5 b are providedwith a solvent feed pipe 13 and a solvent drain pipe 14, respectively.

A downstream end of the solvent feed pipe 13 of the solvent feed line 5a is connected to the residual feed pipe 4 at a location between theresidual pressure-feed pump 10 and the residual drum 9. An upstream endof the solvent feed pipe 13 is connected to a solvent tank or a solventcirculation line, not shown. The organic solvent (e.g. monochlorobenzeneand dichlorobenzene) used as the reaction solvent in the producingprocess of polyisocyanate is held or circulated in the solvent tank orthe solvent circulation line.

A solvent feed valve 15 for feeding or stopping feeding the organicsolvent from the solvent feed pipe 13 to the residual feed pipe 4 isinterposed in the solvent feed pipe 13.

The solvent feed pipe 13 of the solvent feed line 5 a may be connectedto a delivery side (on the downstream side) of the residualpressure-feed pump 10, but it is preferable that the solvent feed pipe13 is connected to a suction side (on the upstream side) of the same tofacilitate pressure rise upon start up of the operation. When the timefor a stable start-up is required, there may be separately provided asolvent drum (not shown) to previously hold the solvent in it for thestart-up of the operation.

An upstream end of the solvent drain pipe 14 of the solvent drain line 5b is connected to the residual feed pipe 14 at a location between theresidual heater 11 and the flash opening and closing valve 12 and in thevicinity of the upstream side of the flash opening and closing valve 12.A downstream end of the same is connected to the solvent tank or thesolvent circulation line mentioned above.

A solvent drain valve 16 for draining or stopping draining the organicsolvent from the residual feed pipe 4 to the solvent drain pipe 14 isinterposed in the solvent drain pipe 14.

In this discomposing system 1, part of the residual feed pipe 4extending at least between the residual pressure-feed pump 10 and theflash opening and closing valve 12 disposed between the solvent feedpipe 13 and the solvent drain pipe 14 serves as the solvent fillingportion 6 of the residual feed pipe 4 connected to the water feed pipe3, for filling the organic solvent via the solvent feed/draining lines5.

Next, the decomposing process of decomposing polyisocyanate residues topolyamine by high temperature and high pressure water using thedecomposing system is described below.

The decomposing process is performed in continuous operation duringwhich the solvent feed valve 15 and the solvent drain valve 16 are bothclosed, without the organic solvent being filled in the solvent fillingportion 6 of the solvent drain pipe 14, while on the other hand, theflash opening and closing valve 12 is kept open.

The polyisocyanate residues temporarily held in the residual drum 9 ispressure-transported through the residual feed pipe 4 by the residualpressure-feed pump 10, flowing toward the water feed pipe 3 via theflash opening and closing valve 12. Further, the polyisocyanate residuesare heated to e.g. 120-180° C. by the residual heater 11. Thepolyisocyanate residues are increased in pressure to a supply pressureof e.g. 5-30 MPa by the residual pressure-feed pump 10 as well as intemperature to a supply temperature of 120-180° C., thereafter beingflown into the water feed pipe 3.

On the other hand, the water flowing in the water feed pipe 3 from thewater feed line is pressure-transported through the water feed pipe 3 bythe water pressure-feed pump 7, flowing toward the hydrolyzer 2, duringwhich the water is heated to e.g. 190-300° C. by the water heater 8. Asa result, the water is increased in pressure to 5-30 MPa as well as intemperature to 190-300° C., thereby to become a high temperature andhigh pressure water. Then, the high temperature and high pressure waterthus produced is flown into the hydrolyzer 2 together with thepolyisocyanate residues coming from the residual feed pipe 4.

The hydrolyzer 2 is controlled so that an inner temperature (thedecomposing temperature) can be set at e.g. 190-300° C. and an innerpressure (the decomposing pressure) can be set at e.g. 5-30 MPa.Further, a hydrolytic ratio (a weight ratio of (high temperature andhigh pressure water/polyisocyanate residues)) is controlled to e.g.0.5-5 under control of the residual pressure-feed pump 10 and the waterpressure-feed pump 7.

As a result of this, in the hydrolyzer 2, the polyisocyanate residuesare hydrolyzed by the high temperature and high pressure water toproduce corresponding polyamine as a decomposition product, while carbondioxide, water, etc. are produced secondarily.

Polyamines include, for example, polymethylenepolyphenylene polyamine(MDA) corresponding to polymethylenepolyphenylene polyisocyanate (MDI),tolylene diamine (TDA) corresponding to tolylene diisocyanate (TDI),xylylene diamine (XDA) corresponding to xylylenedi isocyanate (XDI),tetramethylxylylene diamine (TMXDA) corresponding to tetramethylxylylenediisocyanate (TMXDI), bis(aminomethyl) norbornane (NBDA) correspondingto bis(isocyanatomethyl) norbornane (NBDI),3-aminomethyl-3,5,5-trimethylcyclohexyl amine (IPDA) corresponding to3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI),4,4′-methylenebis(cyclohexylamine) (H₁₂MDA) corresponding to4,4′-methylenebis(cyclohexylisocyanate) (H₁₂MDI), bis(aminomethyl)cyclohexane (H₆XDA) corresponding to bis(isocyanatomethyl) cyclohexane(H₆XDI), and hexamethylene diamine (HDA) corresponding to hexamethylenediisocyanate (HDI).

Then, after the decomposition products drained from the hydrolyzer 2 isreduced in pressure to the atmospheric pressure, the decompositionproducts are separated to each in a dehydrating column not shown, andpolyamine is collected. The polyamine thus collected is reused aspolyamine of raw material in the producing process for polyisocyanate.

Although such decomposing process is performed in continuous operationas mentioned above, the continuous operation is brought to a halt, forexample, before and during a maintenance, and after the maintenance, thecontinuous operation re-starts. In the decomposing system 1, the organicsolvent is previously filled in the solvent filling portion 6 as thestart-up operation upon start up of the continuous operation. Then,after the high temperature and high pressure water is fed from the waterfeed pipe 3 to the hydrolyzer 2, the organic solvent is fed from theresidual feed pipe 4 to the water feed pipe 3, first, and then, thepolyisocyanate residues are fed thereto.

Next, such a start-up operation is described in detail. Before thestart-up operation starts, the decomposing system 1 is at a shutdown.The flash opening and closing valve 12, the solvent feed valve 15, andthe solvent drain valve 16 are closed, and the water pressure-feed pump7, the residual pressure-feed pump 10, the water heater 8, and theresidual heater 11 are at a standstill. Further, the hydrolyzer 2 is notcontrolled in the inner temperature and pressure before the start-up, sothat it is lower in the inner temperature and pressure before thestart-up operation than under the continuous operation.

Upon starting the start-up operation, the solvent feed valve 15 and thesolvent drain valve 16 are first opened to allow the organic solvent toflow into the solvent filling portion 6 of the residual feed pipe 4 fromthe solvent feed pipe 13. At the same time, the polyisocyanate residuesstaying in the solvent filling portion 6 is washed into the solventdrain pipe 14 by the organic solvent flowing into the solvent fillingportion 6, so that the organic solvent is filled therein. Aftercompletion of the filling of the organic solvent in the solvent fillingportion 6, the solvent feed valve 15 and the solvent drain valve 16 areboth closed.

Separately from the above mentioned operation, the water pressure-feedpump 7 and the water heater 8 are brought into operation and thehydrolyzer 2 is controlled, to allow the high temperature and highpressure water to flow into the hydrolyzer 2 from the water feed pipe 3until the predetermined decomposing temperature and pressure for thecontinuous operation mentioned above.

Thereafter, the residual pressure-feed pump 10 and the residual heater11 are brought into operation to pressure-transport the organic solventand the polyisocyanate residues on the suction side (upstream side) ofthe residual feed pump 9 toward the organic solvent filled in thesolvent filling portion 6, so as to increase the inner temperature andpressure of the solvent filling portion 6. Then, the flash valve 12 isopened at the point of time the inner temperature and pressure of thesolvent filling portion 6 exceed the predetermined feed temperature andfeed pressure for the continuous operation mentioned above.

Then, the organic solvent is first fed with at least the predeterminedfeed temperature and pressure for the continuous operation from theresidual feed pipe 4 to the water feed pipe 3, via which the hightemperature and high pressure water is fed to the hydrolyzer 2, with thepredetermined feed temperature and pressure for the continuousoperation. When the organic solvent is fed from the residual feed pipe 4to the water feed pipe 3, a supply flow from the residual feed pipe 4 tothe water feed pipe 3 is formed by the organic solvent fed. A rate ofthe supply flow is, for example, 0.3-3 M/SEC. Then, when the organicsolvent filled in the solvent filling portion 6 and the organic solventon the suction side (upstream side) of the residual pressure-feed pump 9are all fed to the water feed pipe 3, the polyisocyanate residues aresmoothly fed from the residual feed pipe 4 to the water feed pipe 3 withthe same power as that of the organic solvent, going along the supplyflow of the organic solvent. Then, the polyisocyanate residues flowinginto the water feed pipe 3 are fully mixed with the high temperature andhigh pressure water and then fed to the hydrolyzer 2, without stay atthe confluence portion with the water feed pipe 3. This can allow thepolyisocyanate residues and the high temperature and high pressure waterto be mixed with each other at a sufficient linear velocity beforeflowing into the hydrolyzer 2. This can prevent a blockage of the waterfeed pipe 3 which is caused by the production of solid materials growingout of an intermediate product, such as a urea compound, produced by thereaction of the polyisocyanate residues and the high temperature andhigh pressure water. As a result of this, smooth start up of thedecomposing operation can be accomplished.

While the illustrative embodiments of the present invention are providedin the above description, such is for illustrative purpose only and itis not to be construed restrictively. Modification and variation of thepresent invention that will be obvious to those skilled in the art is tobe covered by the following claims.

INDUSTRIAL APPLICABILITY

The decomposing system for polyisocyanate residues and the start-upmethod for the same of the present invention are suitably used forproducing polyisocyanate industrially.

1. A decomposing system for polyisocyanate residues comprising: adecomposing tank for allowing polyisocyanate residues and hightemperature and high pressure water to contact with each other, a waterfeed pipe, connected to the decomposing tank, for feeding the hightemperature and high pressure water to the decomposing tank, a residualfeed pipe, connected to the water feed pipe, for feeding thepolyisocyanate residues to the decomposing tank together with the hightemperature and high pressure water, and solvent filling unit,interposed in the residual feed pipe at a portion thereof connectingwith the water feed pipe, for filling the solvent in the portion.
 2. Thedecomposing system for polyisocyanate residues according to claim 1,which comprises opening and closing unit interposed in the residual feedpipe at an end thereof connecting with the water feed pipe, and residualtransporting unit interposed in the residual feed pipe at a locationthereof on an upstream side of the opening and closing unit, whereinpart of the residual feed pipe extending at least between the openingand closing unit and the residual transporting unit serves as theconnecting portion in which the solvent is filled.
 3. The decomposingsystem for polyisocyanate residues according to claim 2, wherein theopening and closing unit is flash opening and closing unit.